Magnetic disk drives are widely used in computers and data processing systems for storing information in digital form. Digital information is stored in magnetic disk drives as binary-encoded data which is magnetically recorded on a recording surface of a magnetic disk by selective magnetic polarization of regions of the surface of the disk. The recording surface of the magnetic disk is typically divided into narrow annular regions termed "tracks" of different radii. The tracks are assigned numbers to provide addresses for locating data on the recording surface. In modern magnetic disk drives, adjacent tracks are closely spaced--center-to-center separations of adjacent tracks of as little as 50 .mu.m are not uncommon.
Data stored on a magnetic disk is accessed as the disk rotates by means of a transducer called a read/write head. To read data from a rotating magnetic disk, the read/write head produces electronic read signals in response to the passage of magnetic polarized regions on the recording surface of the magnetic disk close by the read/write head as the disk rotates. To write data onto a rotating magnetic disk, the read/write head generates magnetic fields capable of polarizing regions of the recording surface disk passing close by the head in response to the imposition of electronic write signals on the read/write head.
The read/write head is positioned laterally at a radial position in registry with a selected track by means of a read/write head support assembly. In conventional magnetic disk drives, the read/write head support assembly includes a support arm which is connected at one end to a support-arm positioning actuator such as a stepper motor, a rotary voice-coil actuator, or a linear induction motor. The support arm extends over the rotating disk in a cantilevered fashion from a position radially outward of the circumference of the disk. For rigid magnetic disks, the read/write head is typically joined to the end of the support arm opposing the end attached to the positioning actuator by a blade-like read/write-head support finger which is flexible in the direction normal to the recording surface of the disk. An air flow is created adjacent to the recording surface by the rotation of the magnetic disk, which generally causes the read/write head to ride at an aerodynamically-stabilized distance from the surface of the disk. The distance separating the surface of the rotating magnetic disk and the read/write head has been decreasing as the art advances and in some current magnetic disk drives is less than a micrometer.
To read and write data at the high rates required by present-day computer systems, the read/write head must be brought into registry with the track on the magnetic disk to be read from or written into in as short a time as possible. Consequently, the lateral positioning of the read/write head--i.e. positioning parallel to the plane of the recording surface of the magnetic disk--must be done at high speeds. High-speed lateral positioning of the read/write head, however, induces inertial loading of the read/write-head support assembly. Unfortunately, such inertial loading tends to cause the read/write head to overshoot the desired position laterally and tends to excite lateral vibrations in the read/write-head support assembly, especially in the cantilevered support arm of the assembly. Such lateral vibrations are particularly troublesome when the support arm decelerates abruptly to stop. Since the support arm is supported at the end opposite to the end to which the read/write head is connected, the lateral vibrations tend to be greatest in magnitude at the end of the support arm connected to the read/write head. The overshoot and lateral vibrations induced by the inertial loading of the read/write-head support assembly caused by starting accelerations and stopping decelerations of the support assembly tend to lengthen the time required for the read/write head to stabilize at a new position, thereby limiting the speed at which data on the disk may be successfully accessed.
In addition, vibrations in a direction normal to the surface of the disk excited by motion of the support arm may result in collisions between the read/write head and the recording surface of the disk, especially in view of the close separation between the head and the surface of the disk commonly used today. Such collisions can damage the read/write head as well as the disk, leading to downtime, expensive repairs and lost data.
In addition to requirements of high-speed data access, modern magnetic disk drives are subject to size constraints, since digital computers and data processing systems are generally being made smaller. As magnetic disk drives are made more compact, the read/write-head support assemblies tend to be small and intricately shaped. Support arms for the read/write-head support assemblies are frequently made of an aluminum alloy or a magnesium alloy, in part because such materials can readily be fabricated by conventional metal forming and machining techniques into the intricate shapes needed for read/write-head support arms with the dimensional precision required by the need to register the read/write-head accurately with individual ones of the closely-spaced tracks on the magnetic disk.
A property of a material which measures the resistance of a component made from that material to deflection by inertial loads generated by accelerations and decelerations is the "specific stiffness" of the material. Specific stiffness is defined to be the modulus of elasticity (E) of a material under tension divided by the density of the material (.rho.) and can be expressed by the equation: EQU Specific Stiffness=E/.rho..
The specific stiffness value of a particular material is typically represented by "m".
The magnesium and aluminum alloys typically used for making the support arms for the read/write-head support assemblies of magnetic disk drives have specific stiffness values of roughly 2.5.times.10.sup.6 m.
A number of ceramic materials exhibit a higher specific stiffness than conventional magnesium and aluminum alloys. For example, alumina (Al.sub.2 O.sub.3) has a specific stiffness of roughly 9.times.10.sup.6 m and silicon carbide (SiC) has a specific stiffness of roughly 20.times.10.sup.6 m. Although such ceramics have high specific stiffness values, they are generally extremely hard and brittle. It has therefore been impractical, if not impossible, to machine such materials into the intricate shapes required for support arms for the read/write-head support assemblies of magnetic disk drives. Conventional ceramic-forming techniques involving casting and firing to produce support arms of the required shape from such ceramics are also impractical because the variations in dimensions from part to part exceed the required tolerances.
Attempts have been made to combat the problem of vibrations in transducer support assemblies of magnetic disk drives, but heretofore such attempts have met with only limited success.
U.S. Pat. No. 3,769,467 to Gabor discloses a vibration damped transducer head assembly. The transducer head assembly is mounted at the end of a movable arm in a magnetic disk drive unit. An energy-absorbing material is interposed between the transducer head structure and an overhanging mass of relatively dense material. The energy absorbing material becomes lossier as the rapidity of the deforming impulse acting on the absorbing material increases. According to the patent, this tends to dampen vibrations caused by acceleration and deceleration forces generated in operating the disk drive. However, both the energy-absorbing material and the overhanging mass add significantly to the mass of the transducer head assembly, which tends to retard the ability of the assembly to accelerate and decelerate.
U.S. Pat. No. 3,936,881 to Orlando and Weidenhammer discloses an air-damped suspension mechanism for supporting a transducing head in a flexible disk recording device. The suspension system tends to dampen vibrations in the direction generally normal to the disk, but evidently does not dampen lateral vibrations. Moreover, the suspension mechanism requires an air supply system for supplying air to the suspension mechanism at a pressure greater than the surrounding pressure.